Solar cells provide great opportunities for future large-scale electricity generation. However, there are currently significant limitations, such as the relatively low output of most solar cells (typically fifteen percent) and high manufacturing costs.One possible improvement could derive from a new type of solar cell made of semiconductor quantum dots (crystals with dimensions in the nanometer size range). In conventional solar cells, one photon (light particle) can release precisely one electron. The creation of these free electrons ensures that the solar cell works and can provide power. The more electrons released, the higher the output of the solar cell.In some semiconducting nanocrystals, however, one photon can release two or three electron. This is called carrier multiplication. A solar cell based on carrier multiplication could theoretically lead to a maximum output of 44 percent. Moreover, solar cells consisting of nanocrystals can be manufactured relatively cheaply.Carrier multiplication was first measured by researchers at the Los Alamos National Laboratories in 2004. In the last two years, the scientific world has raised doubts about the occurrence of carrier multiplication. Does it really take place or not?Within the Joint Solar Programme of FOM we have now demonstrated that carrier multiplication does indeed occur in lead selenide (PbSe) nanocrystals. This was done using femtosecond pump-probe laser spectroscopy. According to our results, however, the effect in this material is smaller than claimed previously. Despite this, it is still of great promise to exploit carrier multiplication for the next generation of highly efficient solar cells.